Method and apparatus for effecting the discharge of a volatile liquid



April 14,1935 H. zENNl-:R 2,037,673 l METHOD AND APPARTUS FOR EFFECTING THE DISCHARGE OF A VOLATILE LIQUID Filed Jan. 24, 1955 2 Sheets-Sheet 1 MQW ATTORNEYS April 14, 1936. G. H, zENNER 5 2,037,673 METHOD'AND APPARATUS Fon EFFECTING THE DISCHARGE oF A YOLATILE LIQUID Filed Jgn. 24, 1935 sheets-sheet 2 rig-2 NVENTOR TORNEYS Patented v'Apr'. 14, 1936 METHOD AND APPARATS FOR EFFECTING THE DISCHARGE OF A VOLATILE LIQUID George H. Zenner, Bualo, N. Y., assignor, by mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York Application January 24, 1935, Serial No. 3,249

Claims.

This invention relates to a method and ap-` paratus for effecting the discharge of a volatile liquid from a vessel in a closed system against a head of pressure, a'nd particularly of a volatilel liquid, from a final vessel in a system of vesselsy connected in cascade.

The invention has for its object generally the provision of an improved procedure and suitable apparatus for effecting quickly the desired dischargelof very cold volatile liquid which is'obt tained with diiiiculty and at some expense, such as certain liquefied hydrocarbons, liquid'oxygen, liquid nitrogen, and the like, from a vessel, such as a transfer Vessel, to a receiving vessel against a head of pressure.

In transferring volatile liquids of the character indicated which may be partly in the liquid phase and partly in the gas phase, from a supply vessel at a relatively low pressure to a receiver at a relatively high 'pressure in a manner which reduces losses of the gas phase, such as occur to the atmosphere, to a relatively low value;

the resulting condensate augmenting the liquid ultimately discharged. In such cascade system, the discharge of liquid from the vessel operating at highest pressure may become sluggish, particularly at pressures approaching the critical pressure. In the present commercial practice, when transferring liquid oxygen, liquid nitrogen, and the like, the receiving vessel to which the liquid is transferred may have a pressure considerably l in excess of the critical pressure, for example,

the receiver may be at 2100 psi gage.

Specifically, it is an object of the present invention to accelerate the discharge of a low boiling point liquefied gas, such as from a vessel in a cascade system Where the pressure imposed on the liquid passes through or exceeds the critical pressure, in a. manner which achieves the transfer of a desired quantity of liquid in a relatively short period of time.

It is also an object to provide a cascade system of the character lindicated with means for controllably supplying heat in amanner which brings the total internal energy of the contents remaining in a selected vessel after discharge to a relatively low value while maintaining the refrig-4 erating capacity of the material discharged ata relatively high value.

It is a further object to provide vessels in a cascade system with means comprising a connection arranged to absorb heat whereby the energy for effecting the desired discharge is supplied solely as thermal energy, the input thereof being at a rate such as to accelerate the discharge up to substantially any desired value. A connection thus arranged to absorb heat is hereinafter referred to as a thermal leg.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.`

For .a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken inconnection with the accompanying drawings, in which:

Fig. 1 is a view partly in section and partly in elevation showing a simple cascade system having a thermal leg associated therewith for accelerating the discharge of gas material from the system in accordance with the invention; and

Fig. 2 is a similar view showing a modified form of cascade connected transfer vessels ernploying a thermal leg connected to the transfer vessel in a manner which is independent of the liquid withdrawal connection.

`Where liquefied gas is transferred through liquid transfer vessels connected in cascade at successively higher pressures to or beyond the criti- The connection or thermal leg, provided in accordance with the present invention, overcomes this difficulty and communicates with a selected vessel in the transfer system and is arranged to absorb heat from a suitable heat supplying medium, such as water or atmospheric air, in a manner which quickly heats a portion of the liquid being transferred and elevates its temperature to a value above the critical temperature. Such heated material is applied so as to overcome the condition of equal densities of gas and liquid phases; whereby the transfer and discharge of the material is made to take place at a desiredrate. Since the gas remaining after discharge is to be recondensed it is advantageous that the internal energy contained in it be reduced to a relatively low value, at the same time Iit is desired to maintain the refrigeration of the major part of the discharge rela' tively unimpaired which is particularly desired when said refrigeration is to be utilized, as for example,4when the material transferred is to be held in the receiving vessel in the liquid phase or when the refrigeration is to be used for cooling portions of gas.

It is also desired that the heat absorbing element be so arranged that the material is heated to a relatively high temperature in one pass therethrough, the heat being supplied at the appropriate temperature and rate required for accomplishing the heating. When so heated the desired discharge is accomplished and the residual contents of the vessel have a total internal The attainment of a low value for the total' internal energy of the residual contents of the vessel is. an important object of this invention.

The pressure in the vessel after discharge is sub` stantially the same, regardless of the residual gas temperature, so that if this temperature be low the density is high, and vice versa. An increase in temperature of the residual gas not onlycauses an increase in the internal energy per unit weight, 'but also causes the more important decrease in density. As a consequence of this'decrease in density, the totalinternal energy of the residual contents is lower the higher the temperature. By controllably heating the residual gas to a relatively high temperature, a satisfactory low value for the total internal energy is attained.

An advantageous form of thermal leg adapted to this end comprises a heat absorbing element which is in pressure communication at points both above and below the normal liquid level with the vessel from which the material is to be discharged, whereby the material in the liqquickly heated, a volumetric expansion ensues, and a syphonic action takes place. Referring now to the drawings and particu a cascade system which is provided with an inlet connection II adapted to'receive gas material of low boiling point in the liquid phase, for example, liquid oxygen, from' a source of liquid supply at a relatively low pressure. This vessel has a gaseous discharge connection I2 leading from the top and a-liquid discharge connection I3 leading fromthe bottom to another vessel I4 of the system, which, in the arangement shown, comprises the final transfer vesenergy of relatively low value, which results from uid phase which flows into the thermal leg isl larly to Fig. 1, I 0 denotes a transfer vessel in sel of the series transferring the material to a region of high pressure. This second vessel has a gaseous discharge connection I 5 communieating with then upper portion of vessel I0 and liquid discharge connection I6 controlled by valve IGa leading from the lower portion. This connection communicates with a suitable liquid receiving and/or vaporizing device. One form of device' adapted for high pressure service is shown at I8 and discharges material in the gas phase through a service connection I9 to gas storage or consuming apparatus; ingress of material to be vaporized being controlled by an inlet valve as shown at I'I. I

A receiving device that may be used with or without the high pressure device described and adapted to service at relatively low or intermediate pressures is shown at I8', the admission of liquid material thereto being controlled by a valve such as shown at I1' placed in a suitable branch I6' of the liquiddischarge conduit I6 leading from vessel I4. This receiving device has a gas phase discharge conduit I9' and a liquid phase discharge conduit I9".

`The transfer vessels I0 and I4 of the cascade system through which the liquid transferredv passes are constructed so as to preserve the refrigeration of the liquid and to this end are provided with means for rigorously excluding heat from the liquid during transfer. Any suitable means adapted for this purpose may be employed, for example, a heat insulating envelope may be provided as shown on the exterior of each of the vessels; va spaced thin-metal lining or basket may also be employed as shown on the interior of vessel I4. The pipe connections employed are also preferably insulated; the showing of any such insulation in the drawing has been omitted in thel interests of clearness of illustration.

In order that the receiving device may receive liquid material at a desired rapid rate, in accordance with the invention, a thermal leg is connected with the vessel I4 for controllably heating a portion of the liquid therein and raising the pressure of the vessel quickly. The heat'- ing thus practiced is seen to introduce relatively little heat into the discharged material but heats the vaporized material to a temperature such that the total internal energy of the residual contents of vessel I4 after discharge at the desired pressure is lowered. The thermal leg here provided is shown as comprising a heat absorbing element 20 disposed in a heating agent or bath 2l which element preferably has a relatively ex tensive heating'surface; a 'suitable form comprises a plurality of liquid containing tubes, adapted to be immersed in the heating medium of bath 2|, that are joined together by lower and upper headers as shown at 22 and 23. Any arrangement by which the lower header communicates with the lower portion of the vessel I4 may be employed; for example, the header 22 may be directly connected with connection I6 in order to pr vide relatively free communication with the liquid space of vessel I4. 'Ihe upper header 23 is similarly connected to the upper portion of vessel I4, for example, by means ofthe conduit 24 which provides substantiallynnobstructed communication with the upper portion oi the vessel I4 although the conduit preferably has a valve 24a disposed therein. The flow of and 24a. It. should be noted that the heat absorbing element 20 is so arranged in relation tov the vessel I4 that yflow due to the influence of gravity is assured. Thus the column of cold material in conduit ,I6 is more dense and heavier than the column of heated material in element and conduit 24, the diierence in density being great enough to cause flow to occur at the desired rate.

A "gas phase connection is also preferably associated with the gaseous discharge connection I5 that leads to the service connection I9 and is shown at 25. This connection thus has communication at one end with the upper portion of vessel I4 and at the other end with a high pressure source of supply and is controlled by a suitably placed valve a.. Thus arranged the connection 25 serves the twofold purpose of relieving, when desired, the high pressure in the vessel I4 and of initially priming the vessel I4 to permit ilow in receiver I8 when valve Ilia is opened. For example, if an excessive pressure be attained in vessel I4 which is above that in service connection I9, valve 25a. may be opened to permit the passage of material in the gas phase thereinto. If the pressure in vessel I4 be less than that in conduit I9 and valve 25a be opened, the vessel I4 receives gas material in the gas phase which maybe used in priming.

A distributor 26 is preferably placed` in the vessel Il) for introducing heated gaseous material from the vessel I4 when desired. This is accomplished through the branch connection 21 here shown as connected to the relief connection 25 in order to be in communication with the upper part of vessel I4. The admission of gas to the distributor is controlled by means of a valve 21a which is disposed adjacent to the 'valve |50, in

the connection I5 that provides for communication between'the upper portions of the transfer vessels.

The arrangement shown in Fig.v l operates as follows:

Gas material in the liquid phasel from a lo-w pressure source, for example, from a standtank or transport container, is introduced in predetermined amounts through the connection II into the vessel I0, the connection I2 being open during the lling'period. Theintroduction of only apredetermined amount of liquid is secured by associating a suitable metering device with the vessel I0. As shown, this is provided by extending connection I2 into vessel I0 a distance such that it, is sealed by the liquid when the predetermined amount has been introduced.

The transfer of liquid from the vessel I0 to the I4 against whatever pressure there may be in the vessel I4 is effected by first opening the valve 21a to equalize the pressures by condensation' of gas into the liquid charge in vessel Il) and then opening the valves I3a, and I5a. This permits displacementv of liquid from the vessel I8 through the connection I3 and the displacement of gas from the vessel I4 into vessel I0 through the connection 15, When the transfer is complete, the valves I3a, I5a, and 21a are closed.

The operation 'of valve 21ar is practiced in order to accomplish the transfer of liquid material into the vessel I4 with a reduction of the net blowdown loss in accordance with the principle of cascade operation disclosedI in copending application of John J. Murphy, above referred to. Condensation of gas material and equalization of pressures in the vessels I0 and I4 is effected prior ,to the opening of valves I3a and I5a for transferring the material under the force operative in the cascade system, this operative force being any convenient mechanical force, such as gravity.

In the application above referred to, it is shown, that it is desirable to have at a substantially low value the internal energy of the gas which is to be brought intol heat exchanging relation with fresh charges of liquid in accordance with the cascade principle. The means of discharging the gas material from the final vessel in accordance with the present invention accomplishes this end' by heating to a relatively high temperature only the amount of material that is required for displacing the rest at the pressure desired, By heating such amount to high temperature, the total internal energy thereof is at a satisfactory low value.

The transfer of the gas material from the vessel I4 to a receiving device is effected in a manner substantially similar t the transfer from vessel I to vessel I4. For example, the transfer to receiver I8 is accomplished vby first momentarily opening the valve 25a to provide equalization of pressure between vessel I4fand receiver I8, and then opening valves 24a and Ita and nally opening the valve I'I controlling the discharge to the receiver, If, after valve 25a is initially opened for thisv purpose, pressure in vessel I4 rises` above the critical pressure before valves Ita and 24a are opened, the operation is still the same.

Liquid is discharged past valve I1 into the receiver I8, by reason of the higher pressure in vessel I4 and element 28 than in receiver I8. Vessel I4 and element 28 remain at the same pressure by reason of the connections provided, the dis-` charge continuing as long as the input of thermal energy into element 20 causes material therein to expand and generate pressure sufficient to maintain that in vessel I4,.in excess of that in the device I8.

If valve I'I' be opened instead of valve I1, the discharge will be into the device I8', which flow is similarly produced by the maintenance of a pressure in vessel I4 in excess of that in receiver I8. Accordingly, it is seen that pressure is built by means of the element 28 in the vessel I4 above the liquid therein without substantially increasing the sensible heat of the liquid. 'I'his input of thermal energy in the element 28 of the thermal leg may continue elevating the pressure 4in the vessel I4, but it is essential only to elevate the pressure to a point'which produces the desired increase in the rate of discharge of liquid from the vessel I4, i. e., to raise the pressure by an amount over the receiver pressure that just effects the discharge at the desired rate. The initial .pressure may be belowor above the critical pressure depending on the receiver pressure.v 'I'he pressure rise resulting from the thermal leg action is simply dependent on the resistance to ow in the discharge line froml vessel I4 to the receiver. The thermal leg builds up a l diiferential in pressure over that in the receiver and does not necessarily have to produce a wide pressure fluctuation.

` If the receiver pressure is well below criticalpressure, the thermal leg does not in general create a pressure differential such that the pressure at any point is above the critical pressure. Under these conditions, liquid entering the thermal leg is evaporated and then superheated. If the receiver pressure is above the critical pressure,the gas material entering the thermal leg is rapidly heated Pand undergoes a rise in temperature simultaneously with a volumetric expansion with the resultant thermosyphonic action. vA differential pressure above, that in the receiving device results lfrom this expansion which forces the discharge to occur at a rapid rate.

In the event that the pressure in the vessel I4 should rise to excessive values before valve I1 can be opened fully, the excess of pressure in the vessel I4 above that in the discharge line I6 may be quickly relieved by the opening of valve a. The transfer of the liquid from the vessel I4 to the device I8 continues until substantially the whole of the liquid under pressure in the vessel I4 has been discharged. The vessel I4 having discharged its liquid, and all valves being then closed, is ready to receive another charge from the vessel vIll which is effected in the manner above described and the cycle of events repeated.

When discharging liquid toa receiving device of the variety shown at I8', where the material is to be stored in the liquid phase to be later vaporized when desired, it is seen that the present method of eiecting the discharge desirably preserves'the refrigeration in the liquid discharged by heating substantially only the amount of gas material utilized for. building the pressure to a value higher than that of the receiving device which may be located at any elevation relative t the vessel I4.

While the connections, including the heat absorbing element, have been described above as associated with vessels in series cascade relation, whereby there is insured a heat input from an external source to raise the Vpressure without increasing ythe sensible heat of the major portion of the liquid, it is contemplated that a single leg may be associated with other arrangements of vessels in cascade relation; for example, a plurality of vessels operating in series-parallel in order to effect a transfer of a large amount of material substantially continuously with a minimum amount of equipment.7 The series-parallel arrangement admits of this, since one transfer vessel of a. parallel pair is adapted `to be iilled while the other is discharging, and vice versa. An arrangement to this end is shown in Fig. 2.

In Fig. 2, a series parallel arrangement of transfer' vessels is shown which employs a thermal leg connected to the final vessels of each series in a manner entirely independent of the liquid discharge connections. In the first series a vessel 4|I'has an inlet connection 4I for supplying a liquefied gas from a low pressure source, a gas phase outlet 4Z, and a liquid phase outlet 43 which transfers the liquid to another' vessel 44 under the iniluence of a gravity field, there being also a connection 45 leading from the upper portion of the vessel 44 to the upper portion of vessel 40 to permit gas displacement from the vessel 44 when liquid enters it from the vessel 40. A liquid discharge connection 46 leads from vessel 44 and has union with a connection 41 leading to a receiving and'vaporizing device 48 that has a service connection 49 for supplying consuming or storage apparatus.

In another series, which is arranged in parallel with the first, there is a. vessel 50 that has a liquid inlet 5I, a gas phase outlet l52, and a liquid discharge 53 leading to a vessel 54 that is in parallel with vessel 44. A gas phase displacement connection 55 connects the upper portion of vessel 54 with the upper portion of vessel 50 and a liquid discharge connection 56 leads from the bottom part of vessel 54 to make union with the connection 41 in the same manner as does connection 46.

The series-parallel .system of cascaded vessels here shown is preferably provided with acommon thermal leg for accelerating the discharge from the vessels 44 and 54 to the device 48. In

ing medium being admitted to the chamber at any suitable point, for example, through the inlet 58, an exit being provided as shown at 59. The lower header 62 in the element 60 is connected with the lower portion of the vessel 44 by means of a connection 66 that is entirely separate from connection 46, and with the lower portion of vessel 54 by means of a similar connection 66'; this arrangement is facilitated by the provision of a common connection 51 leading to the lower header of the junction of the connections 66 and 66 as shown. A connection 64 leads from the upper header 63 to a junction from which branch connections 65 and 65 lead respectively to the gas phase displacement connections 45 and 55.

The connections 65 and 65' are arranged always to be in relatively free and unobstructed communication with the gas space of the vessels 44 and 54. Accordingly, the valves 45a and 455a which control the connections 45 and 55 are disposed above the junction points where connections 65 and 65 meet the connections 45 and 55 respectively. Valves 43a and 53a are shown respectively in the liquid transfer connections 43 and 53. Similarly, valves are shown at 46a. and 56a in the liquid discharge connections 46 and 56. Valves controlling the thermal leg are shown at 66a in theconnection 66 and at 6612 in the connection 66. A gas phase connection 68 leading from the junction of conduits 65 and 65' is arrangedl to communicate with service conduit 49, and may with advantage be provided with a suitable check-valve to permit one-way discharge into the service conduit, for example, with a spring-loaded check valve as shown at 69.

Means for cross-equalization of pressures between vessels in parallel are' provided by a connectionlll controlled by valve 10a, which connects discharge conduits 46 and 56 so as to pro-l vide ommunication between the liquid spaces of vessels 44 and 54 and by a connection 1I ,controlled by valve 1Ia which connection joins distributors 12 and 12 that are disposed in the lower portions of vessels 40 and 50.

In this arrangement, the operation of the cascaded vessels'40, 44, 50, and 54 which discharge into the receiving device 48 is substantially similar to the series system shown in Fig. 1 except the parallel arrangement provides additional steps of equalization and permits substantially continuous operation, i. e., when the vessel 40 is being filled with liquid, the vessel 44 is transferis being drained into vessel 54. When a charge from vessel40 is transferred to the vessel 44, the vessel 50 receives a charge through the inlet 5I, the vessel at 54, transferring its charge to device 48, is filled with gas at high pressure. Between these rfilling and discharging events, cross-equalizations are effected by opening the valves 10a and 1Ia.

Ii it is desired to discharge liquid into the vaporizer, for example, from vessel 44, when just filled, the connection 10 is 4opened by opening valve 10a to equalize pressures, gas iiowing from vessel 54 through the liquid in vessel 44 after which valve 10a is closed and valve 46a is opened,

which brings pressure in vessel 44 up to that in device 48. 'Ihe thermal leg connection of the element 6l) to the vessel 54 having been shut off previous to cross-equalization by closing valves 65h and 66D, the corresponding connections to the vessel 44 are now opened, i. e., valves 66a and 65a are opened. When the liquid in vessel 44 is fully discharged,'valves 66a and 65a'are closed together with valve 46a andthe steps of crossequalization and discharge by means of the thermal leg are repeated for vessel 54. The heat absorbing element is thus seen to be in substantially continuous operation, building pressure alternately in vessels 44 and 54. In'a system .of

three or more vessels in parallel, the period between successive discharges is still further reduced in duration. yIn the event that pressure should build to an excessive value in either oi. the vessels 44 or 54 while connected to thermal leg 60, safe exit is provided'through the conduit 68 and the automatic opening of valve 69.

Here itis seen that by properly timing the events4 charge alternately into the device 48.

An operator, of course, may acquire considerable skill -in effecting these events so that this transfer takes place in a minimum of time. It is preferable, however, and in the practice of the invention it is contemplated that the valves shall be automatically operated. It will beunderstood, therefore, that in the practice of the invention, motor-operated' valves of a suitable type will be substituted for the valves shown at I la, IZa, I3a, 15a, Isa, etc., or those shown at 4Ia, 42a, 43a, 45a, 46a, etc.; the actuation of the valves being under the control of any suitable master actuator. These features, however, are Ano part of the present invention and while in practice they may be incorporated, in a commercial'device and 'make for the eiiiciency thereof, the principle by which pressure is built to accelerate discharge by means of a thermal leg is in no wise altered thereby, the acceleration of the discharge contemplated being effected by the rate of energy input into the thermal leg as well as by the rate of ow of'uid into the thermal leg, and not by the periods which elapse between events in the cycle of operations practiced.

Since certain changes in carrying out the above process and in the constructions set forth, which` in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.l

Having described my invention, what I claim is new and desire to secure by Letters Patent is:

1. A method of eii'ecting the discharge of liquid oxygen from a nal transfer vessel in a cascade system to a receiver at a relatively high pressure, which comprises lling the vessel with a predetermined charge of liquid oxygen, momentarily admitting gaseous oxygen to said vessel, conveying a portion of said charge of liquid oxygen to a heating device while maintainingthe same in pressure communication with said charge at points both above and below the liquid level,

supplying thermal energy to said heating device suicient to cause expansion '.of said portion and generate pressure in excess of said relatively high pressure whereby the remainder of the body in said vessel is expelled, and maintaining the iinal temperature of the heated portion remaining in said vessel at a relatively high value while the total internal energy is at a satisfactory low value.

2. Amethod of eiecting the discharge of liquid oxygen from a nal transfer vessel in a cascade system toa receiver at a pressure equal to or in excess of the critical pressure, which comprises charging the vessel with a predetermined quantity of liquid oxygen, momentarily admitting gaseous oxygen from a high pressure source, conveying a portion of the charge of liquid oxygen to a heating device, maintaining said portion in pressure communication with the remainder of said charge at points both above and below the liquid level, supplying thermal energy to said heating'device tolan extent. which produces an expansion of said portion and generates a pressure which builds t'o a value in excess of the critical pressure whereby the remainder of said charge may be expelled from said vessel at a desired rate, and maintaining the final temperature of the heated portion remaining in said vessel at a relatively high value while the total internalenergy is at a satisfactory low value.

u 3. A method of effecting the discharge of a volatile liquid having a boiling point materially below 273 K. from an insulated vessel into a receiver with self-compression of the gas phase evolved, which comprises segregating and controllably heating a `portion of each body of liquid being discharged to elevate its pressure while maintaining the temperature of the remainder of said body below that of said heated portion, expelling said remainder to receivers, and subjecting the heated gaseous portion remaining in said vessel to intimatecontact with other segregated bodies of liquefied gas whereby a desired portion of the gaseous remainder is condensed.

4. A method of effecting the discharge of a volatile liquid having a boiling point materially below 273 K. from a system to a receiver at a relatively high pressure, which comprises segre- -gating a succession ofbodies of said volatile liquid, separating and controllably heating a portion of each of .said bodies to an extent suiicient to generate pressures above said bodies to values in excess of that in said receiver, applying said pressures to effect' discharge of said bodies into said receiver, and conducting the gaseous remainder of each of said bodies into another body of said volatile liquidwhereby a portion of said remainder is condensed and combined with said other body.

5. A method of eiecting the discharge of a volatile liquid having a boiling point materially below 273 K. from an insulated vessel in a cascade system and forcing it as Vgaseous material into a receiver at a pressure and temperature in excess of its critical pressure and temperature solely b'y the input of thermal energy, which method comprises segregating a succession of bodies of said volatile liquid, subjecting each of said bodies to a plurality of stages of increased pressure, discharging fluid from the final stages of increased pressure into said receiver by controllably introducing thermal energy to isolated portions of leach of said bodies whereby said portions are converted to a gas phase, redistributing said porenergy introduced in said nal stage among the initial stages in a manner such that said thermal energy istransferred from the gaseous material to the bodies of material in the initial stages, and reconverting a portion of said gaseous material to the liquid phase for use.`

6. A method of transferring a liquefied gas from a'supply container at relatively low pressure 4to a receiver at a relatively high pressure, which comprises withdrawing a succession of metered charges from said container into a transeach of said charges while in pressure communi-l cation with the remainder to an extentsuilicent to elevate the pressure on each of said charges to a value exceeding that in said receiver, discharging the remainder of each of said charges into said receiver under the influence of said generated pressure, and excluding substantially all heat of external origin from'the remainders of said charges.

8. In a cascade system of the -character described, the combination with a plurality of associated vessels arranged to transfer a volatile liquid material, at least one of which is arranged to discharge said material against a relatively high pressure, of a receiver adapted to receive said discharge, means for withdrawing liquid from said high pressure vessel and conveying the same to said receiver, and controllable heating means for withdrawing a portion of liquid connected` to communicate with said vessel discharging against high pressure at points both above and below the normal liquid level of-said vessel, said last named means including a heat absorbing element having a relatively extended heating surface. Y

9. In a cascade system of the character described, the combination with a. plurality of as' sociated vessels arranged to transfer a volatile liquid -mater'ial, one of said vessels being arranged nally to hold and discharge said material, of a receiver at a relatively high pressure vfor receiving said discharge, means for withdrawing liquid from said vessel and conveying the same to said receiver,a connection communicating with said vessel at points bothyabove and below the normal liquid level and including a controllable heat absorbing element having a relatively ex' l tended heating surface, and means associated with said element f or supplying a heating agent in contact with said heating surface.

10. In a cascade system of the character described, vthe combination with a plurality of vesing a heat absorbing element having a relatively extended heating surface and positioned below the normal liquid level, a relatively unobstructed connection leading from said element from a 'point in the vessel above the normal liquid level therein, means for supplying aheating agent in thermal contact with said surface whereby pressure may be builtin the gas space of said vessel in excess of the pressure of said receiver, and

means for equalizing gas pressures in the series connected vessels arranged to eiect heat exchange between gas and liquid when equalization takes place.

11. In apparatus for vtransferring a volatile liquid material, the combination with a supply container at a relatively low pressure, of a receiver at a relatively high pressure, an intermediate transfer vesselarranged to receive and hold uid material, the combination with a supply container at a relatively low pressure, of a receiver at a. relatively high pressure, an intermediate V transfer vessel arranged to receive and hold a metered charge of liquid from said supply container, a thermal leg in communication with said vessel at points above and below the normal liquid level therein, a. priming connection adapted to admit gasy at high pressure from said receiver to said vessel, means for conveying the balance of said charge to said receiver, means associated with said thermal leg for controllably heating the withdrawn portion whereby pressures in excess of that" in said receiver may be generated in said vessel, and means associated with said vessel for s excluding heat other than that controllably introduced.

13. In apparatus for transferring a volatile liquid material, the combination with a supply container at relatively low pressure, of a receiver at a relatively high pressure, a transfer vessel interposed between said container and receiver and arranged to receive and hold a succession of metered charges of the liquid supplied from said container, a thermal leg in fluid communication -with said transfer vessel at points yabove and below the normal liquid level therein whereby a portion of a charge in said vessel may be withdrawn, meansfor conveying the balance of a chargel in said vessel to said receiver, means associated with said thermal leg for controllably heating said withdrawn portion, said thermal leg and heating means being proportioned to supply the energy required to force said remainder into said receiver in a desired period of time, and means for excluding heat from the portion transferred other than that controllably introduced in said thermal leg.

14. A method of effecting discharge of a volatile liquid having a boiling -point materially below 273 K. from a selected vessel in a; cascade system discharging to a receiver at a relatively high pressure, which comprises, filling said vessel successively with bodies of predetermined volume of the. liquid to be transferred, withdrawing and controliably heating a portion of each of said bodies to an extent which causes expansion and produces a pressure for expelling the remainder of the body in a desired period of time, and causing the gaseous remainder to pass in thermal contact with another body of the liquid being transferred.

15. A method of eiecting the discharge of liquid oxygen from a selected vessel in a cascade system discharging to a vaporizer, which comprises liing said vessel successively with bodies of liquid oxygen intended to be transferred,

withdrawing and controllably heating a portion.l of each of said bodies to an extent such that pressure is generated in excess of that in the va..- porizer to which the remainder of said body is supplied, the gaseous remainder being heated to a relatively high value while the total internal energy `associated with said charge is at a satisfactory low value, and subjecting the gaseous remainder to heat exchange treatment with an 10 incoming body of liquid oxygen.

GEORGE H. ZENNER. 

